The disclosed embodiments generally relate to methods and systems for printer color management in image/text printing or display systems. The embodiments are directed to processes for generating improved spot color accuracy.
To meet customer demand, the commercial printing industry requires the capability of producing spot colors accurately and consistently. Spot colors can be defined as a fixed set of colors which may be Pantone® colors, customer logo colors, colors in a customer's proprietary marked patterns, or customer defined colors in the form of an index color table. Spot colors are often used, or can be used, for large background areas, which may be the most color critical portion of a particular page. Consistent color in these areas may determine the difference between success and failure in meeting customer requirements. Customer demands for color accuracy and consistency are typically much tighter for spot colors than for colors within images.
Existing spot color editors for color printers utilize a manual approach to the adjustment of CMYK combinations of spot colors, for example, prior to raster image processing (RIPing). For example, the document creator may select a Pantone® color for application in specific areas through a user interface on a printing device or computer monitor, such as that available on the Xerox® DocuSP® Controller. The Pantone-provided CMYK combination for the selected printer is obtained from a look-up table. Prior to RIPing the document in the printer, the operator has the option of entering a spot color editor function and specifying an alternative CMYK combination to achieve the desired color. The document is then RIPed and then printed using the spot color editor combinations where specified, and Pantone combinations otherwise.
In addition to spot color editors based on Pantone® colors as discussed above, custom spot color formulas, described in percentage of colorants such as CMYK for a particular color, are sometimes provided by a user of a printing device to print a custom color, also referred to as a named custom spot color.
One problem associated with conventional printing systems which include functionality for a user to create custom spot colors is associated with the ability of the printing device to operate in one of a plurality of states/modes, where each state/mode of the printing device is capable of printing a distinct gamut volume of colors. Consequently, a user specifies a formula for a custom spot color while the printing device is operating in one state, which provides one gamut, and in the event a second state of the printing device is used to complete a print job utilizing the custom spot color, a second gamut distinct from the first gamut is utilized, which may not print the custom spot color as desired by the user.
For some customers, the process of manually adjusting spot colors is far too difficult or time consuming. These customers will always use the built-in static CMYK spot color dictionary and are forced to accept the potentially large accuracy errors that can occur with long term printer variation.
This disclosure provides a method and system to provide editing of multiple custom spot color tables to maintain custom spot color rendering consistency across multiple states of a printing device.
All U.S. patents and published U.S. patent applications cited herein are fully incorporated by reference. The following patents or publications are noted:
U.S. Patent Application Publication No. 2002/0093684 to Bares et al. (“Accurate Printing of Proprietary Mark Patterns and Colors”) describes a printing system that provides a dictionary of recognizable patterns and defined colors corresponding to proprietary marks and selected colors. The dictionary is linked to a user interface on which a user may designate a location within a document and one or more of the proprietary marks with defined colors from an accessible menu. A processor associates the defined colors with the image at the specified location and generates a printer signal representative of the colors and image. Alternatively, the processor may include a pattern recognizer for identifying recognizable patterns within a document. Those patterns having a likeness to defined patterns within the pattern dictionary can be converted to the defined patterns for display or imaging.
U.S. Pat. No. 6,157,469 to Mestha (“Dynamic Device Independent Image Correction Method and Apparatus”) describes a method of controlling color drift between a desired image and an output image as obtained by a marking device and intended to match the desired image. The method includes detecting a current output color in the output image with a color sensing device, determining a difference between the current output color in the output image and a corresponding color in the desired image, and automatically setting a next output color in the output image equal to a corrected color that minimizes the difference between the next output color and the corresponding color in the output image.
U.S. Pat. No. 6,178,007 to Harrington (“Method for Continuous Incremental Color Calibration for Color Document Output Terminals”) teaches a method for continuously upgrading the color calibration for an electrophotographic printer using a color transform look up table stored in memory. A single or small number of color patch samples is printed at regular intervals during the use of the printing machine. The color patches are sensed and a determination made as to the difference between the sensed color and the desired color. A corrective color calibration value is determined for the sensed patch and a correction is made for that color in the printer memory. The process is repeated to assure that all of the colors within the gamut of the machine are continuously updated.
U.S. Pat. No. 6,744,531 to Mestha et al. (“Color Adjustment Apparatus and Method”) teaches an apparatus for providing consistent output across a plurality of different hard copy output devices which may be included in a system having an image data source and a hard copy output device. The image data source supplies image data to a printable image data adjusting apparatus. The image data supplied may be in a device-dependent color space or a device-independent color space. For image data in a device-dependent color space, the adjusting apparatus first converts the image data into device-independent image data and stores it in memory as target image data. If the image data is already device-independent, the image data are stored in the memory of the adjusting apparatus as target image data. The printable image data adjusting apparatus then uses the target image data to generate printable image data. The hard copy output device uses the printable image data to generate a hard copy image. The hard copy image is then passed within the optical field of a sensor that detects device-independent image data values of the hard copy image. The detected device-independent image data values are then compared against the target image data to generate color adjustment factors. The color adjustment factors are used to produce a hard copy image having detected device-independent image data values that more closely represent the target image data.
U.S. Pat. No. 7,069,164 to Viturro et al. (“Method for Calibrating a Marking System to Maintain Color Output Consistency Across Multiple Printers”) teaches a method for maintaining consistent color output across printers even when the inline sensors have differences in accuracy due to various technical and environmental factors. A spectro-photometer is used to measure the color quality of printed references. Adjustments are then iteratively made until reference charts of desired color quality are obtained. The printed reference allows one to achieve relatively high system performance by removing sensor inaccuracies. Using the printed reference measured by the inline sensor, control systems of each machine are calibrated. At customer sites and at suitable intervals, a reference document can be read using the inline sensor on a reference machine and any differences from expected values can be calibrated out.
U.S. Patent Application Publication No. 2005/0030560 to Maltz et al. (“Methods and Systems for Controlling Out-of-gamut Memory and Index Colors”) describes methods and systems in an image processing device for controlling colors that are located external to a gamut. A plurality of color values can be automatically provided as input to said image processing device, wherein the image processing device is under the control of a particular dimensional order, typically a three-dimensional order, but alternatively can be a two-dimensional order. An operation can then be performed dynamically determining which color value among the plurality of color values has attained a gamut limit. Thereafter, the particular dimensional order can be automatically reduced, providing improved control for colors that are located external to the gamut. The plurality of color values analyzed is generally associated with three colors: cyan, magenta, and yellow.